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5.  Cyanates.—The salt is triturated with about 84% alcohol, filtered
and concentrated, and hydrochloric acid added :  if cyanate were, present,
effervescence will occur.

6.  Thiocyanates, Ferrocyanides.—-The i : 10 solution is tested with
a few drops of ferric chloride, which gives a red coloration with thiocyanates
and a blue precipitate with ferrocyanides.

7.  Chlorides.—<i gram is mixed with 2 grams of nitre and 10 grams
of pure potassium carbonate and fused to decompose the cyanide, the fused
mass being dissolved in water, acidified with nitric acid and tested with
silver nitrate.

8.  Soda.—i gram is evaporated to dryness with excess of hydrochloric
acid (in a good draught), the residue being dissolved in a little, water and
tested for sodium by the flame or by means of potassium pyroanthnoniate.

9.  Heavy Metals.—'The  i : 10  solution is boiled with  hydrochloric
acid until all the hydrocyanic acid is expelled (in a {rood draught] and then
tested with hydrogen sulphide, with subsequent addition of ammonia.

10.  Quantitative Determination.—-10 grams are dissolved in water
and the solution made up to a litre ; to 25 e.c. of the solution (   • 0-25 gram
of substance) are added a crystal of sodium chloride and N/ro-silver nitrate
then run in from a burette until a persistent turbidity is obtained.    The
number of c.c. used, multiplied by 5-2, gives the. percentage of KCN in the
sample. -l

Chemically pure potassium cyanide contains about oy% KCN ; the, com-
mercial pure product and that for technical purposes contain considerably less
(only up to 50%). The commercial salt often contains marked proportions of
sodium cyanide and when this is calculated as potassium cyanide, the content
of the latter appears greater than the true values (sometimes even greater than
100%) ; in such cases the soda may be determined, proceeding as in 8 (above)
and then testing the alkali chlorides by the ordinary methods (sc-fl Fertilisers,
Stassfurt Salts).


Ka('Ta(')7   ::•:  '2(}<!\:2

Orange red crystals soluble in water. The commercial Hall, is usually
pure or almost so, only containing small quantities of sulphates and of
residue insoluble in water. It may, however, contain also chlorides, lime
and magnesia and. may be adulterated with sodium didmmiate (especially
when powdered). Its value depends essentially on the content of real
dichromate or of chromic anhydride. The analysis includes, therefore,
the following tests and determinations :

1. Sulphates.—3 grams, dissolved in 100 c.c. of water, acidified with

1 When .silver nitrate acts on. potassium cyanide, it gives first: the soluble double
cyanide of potassium and silver:

AgNO3 -I- 2'KCN    • KAg(ON)a •)• KNO., ;

as soon, however, as the silver nitrate is in excess, it reacts with tin* sodium chloride
forming insoluble silver chloride.

If the sample contains appreciable proportions of sulphides, titration with silver
nitrate is preceded by agitation of the solution with powdered lead carbonate ami
filtration,ng the alcohol (greendichromate in the solution determined iodometrically. XV, z, p, 32j, and Hull, chim. /arm,,